Cancer chemoprevention is the use of natural, synthetic or biologic chemical agents to reverse, suppress, or prevent carcinogenic progression to invasive cancer. Recent clinical trials in preventing cancer in high-risk populations suggest that chemopreventive therapy is a realistic treatment for high-risk patients. Chemopreventive therapy is based on the concepts of multifocal field carcinogenesis and multistep carcinogenesis. In field carcinogenesis, generalized carcinogen exposure throughout the tissue field results in diffuse epithelial injury in tissue and clonal proliferation of the mutated cells. These genetic mutations throughout the field increase the likelihood that one or more premalignant or malignant lesions may develop in the field. Multistep carcinogenesis in the stepwise accumulation of these genetic and phenotypic alterations. Arresting one or more steps in the multistep carcinogenesis may impede or prevent the development of cancer. See generally Tsao et al., CA Cancer J Clin 54:150-180 (2004).
Azurin, and other cupredoxins, are cytotoxic specifically towards cancer cells. Azurin induces apoptosis in J774 lung cancer cells. Yamada et al., PNAS 99(22):14098-14103 (2002). On entry into J774 lung cancer cells, azurin localizes in the cytosol and nuclear fractions, and forms a complex with tumor suppressor protein p53, thereby stabilizing it and enhancing its intracellular level. Id. The induction of azurin-mediated apoptosis is not limited to J774 cells. Azurin can also enter cancer cells such as human melanoma UISO-Mel-2, human breast cancer MCF-7 cells, and osteosarcoma. Yamada et al., Infect Immun. 70:7054-7062 (2002); Punj et al., Oncogene. 23:2367-2378 (2004). Azurin allowed the elevation of the intracellular p53 levels, leading to enhanced Bax formation and induction of apoptosis in such cells. Most interestingly, intraperitoneal injection of azurin in nude mice harboring xenografted Mel-2 or MCF-7 human cancers led to statistically significant regression of such cancers. Id.
The mouse mammary gland organ culture (MMOC) model has been fairly well established to study effects of hormonal regulation of mammary gland development and epithelial cell transformation. The MMOC assay may be used to evaluate the inhibitory effects of potential chemopreventive agents on both hormone-induced structural differentiation of mammary glands and on the development of DMBA-induced preneoplastic hyperplastic alveolar nodule-like lesions in the gland. Mammary glands respond to hormones in organ cultures to differentiate into alveolar structures or for inducing expression of casein and a-lactalbumin. Mammary glands from young, virgin animals, when incubated for 6 days in the presence of insulin (I)+prolactin (P)+aldosterone (A), can differentiate into fully-grown glands. These glands morphologically resemble the glands obtained from pregnant mice. Aldosterone can be replaced by estrogen (E)+progesterone (Pg). Inclusion of hydrocortisone (H) to the medium stimulates the functional differentiation of the mammary glands. Mehta and Banerjee, Acta Endocrinol. 80:501 (1975); Mehta and Moon, Breast Cancer: Treatment and Prognosis 300, 300 (Basil A Stoll ed., Blackwell Press 1986). Thus, the hormone-induced structural and functional differentiation, observed in this culture system, mimics the responses to hormones observed during various physiological stages of the animal.
Mice exhibit a distinct preneoplastic stage prior to cancer formation in MMOC. Such preneoplastic lesions in C3H mice are induced by murine mammary tumor virus or in BALB/c mice by DMBA. Exposure of the glands to 2 μg/ml DMBA between days 3 and 4 of growth phases followed by regression of the glands for 2-3 weeks in the medium containing only insulin, results in the formation of mammary alveolar lesions (MAL). Hawthorne et al., Pharmaceutical Biology 40:70-74 (2002); Mehta et al., Methods in Cell Science 19:19-24 (1997). Furthermore, transplantation of epithelial cells, prepared from glands containing the DMBA-induced mammary lesions, into syngeneic host resulted in the development of mammary adenocarcinoma. Telang et al., PNAS 76:5886-5890 (1979). Pathologically, these tumors were similar to those observed in vivo when mice of the same strain are administered DMBA. Id.
DMBA-induced mammary lesion formation in MMOC can be inhibited by a variety of classes of chemopreventive agents such as retinoids. These agents include chemopreventive agents derived from the natural products such as brassinin and resveretrol, thiols, antioxidants, inhibitors of ornithine decarboxylase such as OFMO and deguelin, inhibitors of prostaglandin synthesis, Ca regulators, etc. Jang et al., Science 275:218-220 (1997); Mehta, Eur. J. Cancer 36: 1275-1282 (2000); Metha et al., J. Natl. Cancer Inst. 89:212-219 (1997). These studies clearly demonstrate that this organ culture system offers a unique model to determine the effectiveness of compounds against mammary carcinogenesis. The results can be expected to closely correlate to the inhibition obtained by in vivo administration of such compounds.
In the presence of aldosterone and hydrocortisone, and in the absence of estrogen and progesterone, the MMOC can be induced to develop estrogen independent MAL. The MMOC may also be induced to form mammary ductal lesions (MDL). The MDL can be induced if estrogen and progesterone instead of aldosterone and hydrocortisone are included in the medium. The alveolar structures in the presence of ovarian steroids are very small but the intraductal lesions are observed in histopathological sections. Mehta et al., J. Natl. Cancer Inst. 93:1103-1106 (2001). The antiestrogens, which selectively work on ovarian hormone dependent ER+breast cancers such as Tamoxifen, inhibited MDL formation and not MAL. Thus, this modified culture model in addition to conventional MAL induction protocol now can be used to evaluate effects of chemopreventive agents on both MAL and MDL.
In chemically transformed experimental MMOC models, p53 is rarely mutated or altered, but inactivation of p53 leads to increased aneuploidy in tumors. Further studies in mice bearing C3(1)-Tag transgene suggested that abrogation of p53 function can be a critical event in tumor formation even in the presence of oncogenes. Studies have shown that p53 is inactivated or suppressed by estrogen. Thus, this model can be used to evaluate the effects of azurin on the development of premalignant lesions and the ability of azurin to modulate p53 expression in mammary epithelial cells. This model can also be used to evaluate the effect of estrogen receptor (ER) inhibiting compounds in combination with azurin.